WO2014022388A1 - Method of improving photoluminescence of silicon nanoparticles - Google Patents
Method of improving photoluminescence of silicon nanoparticles Download PDFInfo
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- WO2014022388A1 WO2014022388A1 PCT/US2013/052717 US2013052717W WO2014022388A1 WO 2014022388 A1 WO2014022388 A1 WO 2014022388A1 US 2013052717 W US2013052717 W US 2013052717W WO 2014022388 A1 WO2014022388 A1 WO 2014022388A1
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- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
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- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/59—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing silicon
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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- C01P2004/60—Particles characterised by their size
- C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
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- C—CHEMISTRY; METALLURGY
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- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
Definitions
- This disclosure relates generally to silicon nanoparticles. More specifically, this disclosure relates to a method of enhancing the photoluminescence of silicon nanoparticles and the silicon nanoparticle compositions resulting therefrom.
- silicon nanoparticles are photoluminescent in visible light when stimulated by a source of lower wavelength light. This is thought to be caused by a quantum confinement effect that occurs when the diameter of the nanoparticle is smaller than the exciton radius, which results in bandgap bending (i.e., increasing of the gap).
- silicon is an indirect bandgap semiconductor in bulk
- silicon nanoparticles having a diameter below five nanometers emulate a direct bandgap material. Since direct bandgap materials can be used in optoelectronic applications, silicon nanoparticles have the potential to become a key material for use in future optoelectronic applications.
- the preparation of nanoparticles with surface properties that allow for prolonged stabilization, i.e., minimize agglomeration, and that also exhibit maximum emission intensity and luminescent quantum efficiency has been and still is a persistent challenge.
- the very high frequency allows for the coupling between the radio frequency (rf) power and the discharge to produce a high ion density and ion energy plasma.
- rf radio frequency
- Such a capacitively coupled system requires a relatively high input power ( ⁇ 200 W) in order to provide plasma that exhibits even modest power ( ⁇ 5 W) because a large amount of the input radiofrequency power is reflected back to the power supply.
- the present disclosure provides a method of enhancing the photoluminescence of silicon nanoparticles.
- the present invention relates to a method of improving the photoluminescence of silicon nanoparticles and to the compositions of silicon nanoparticles prepared therefrom.
- the method comprises exposing a composition comprising silicon nanoparticles having a mean particle diameter not greater than 5 nm and a fluid to a non-ambient condition selected from (i) elevated temperature, (ii) elevated humidity, (iii) elevated pressure exerted by an oxygen-containing gas, (iv) a hydrogen plasma, (v) hydrogen gas, (vi) ultraviolet radiation, and (vii) and a combination of at least two of (i)-(vi).
- the silicon nanoparticles may be prepared by a gas phase reaction.
- a composition comprising silicon nanoparticles and a fluid may be prepared by forming the silicon nanoparticles in a low pressure high frequency pulsed plasma reactor and collecting the nanoparticles in a capture fluid with in the reactor.
- the exposure of the silicon nanoparticle compositions to molecular hydrogen, hydrogen plasma, ultraviolet radiation, elevated temperature, elevated humidity, and/or elevated pressure results in improved photoluminescence.
- the exposed or treated nanoparticles exhibit increased maximum emission intensity and luminescent quantum efficiency.
- these improvements are accompanied by a blue shift in the emitted light to a shorter wavelength.
- the composition Prior to exposing the composition to a non-ambient condition, the composition may, when desired, be exposed to ambient temperature, pressure, relative humidity, and air.
- the composition is exposed to the non-ambient condition for an amount of time sufficient to increase the maximum emission intensity of the composition when excited by light having a wavelength of from 190 to 600 nm.
- the non- ambient condition is a combination of two different conditions includes exposure of the silicon nanoparticle composition to both elevated temperature and elevated humidity.
- the elevated temperature ranges from above ambient temperature up to the boiling point of the fluid; and the elevated humidity ranges from 30 to 100% relative humidity (RH).
- non- ambient condition represents a combination of conditions
- an oxygen-containing gas such as oxygen or air.
- the elevated temperature ranges from above ambient temperature up to the boiling point of the fluid and the elevated pressure is greater than atmospheric pressure.
- the elevated pressure is between atmospheric pressure and 4,000 psig (2.768 x 10 7 Pa).
- the silicon nanoparticle compositions prepared according to the method(s) described herein comprise a plurality of silicon nanoparticles having a diameter that is not greater than 5 nm dispersed in a fluid.
- the concentration of the silicon nanoparticles in the fluid that make up the silicon nanoparticle composition is greater than 0.0001% (w/w) and less than 50% (w/w).
- the concentration of the nanoparticles in the composition is selected such that the agglomeration of nanoparticles in the selected fluid is minimized.
- the fluid may be comprised of a solvent, a silicone fluid, or a mixture thereof.
- a silicone fluid it is selected as one from the group of a polydimethylsiloxane, phenylmethyl dimethyl cyclosiloxane, tetramethyltetraphenyl- trisiloxane, pentaphenyltrimethyltri-siloxane, and mixtures or compositions thereof.
- the silicon nanoparticles may comprise silicon, a silicon alloy, or a mixture thereof.
- a silicon alloy is generally comprised of silicon and an element selected from at least one of germanium, boron, phosphorous, and nitrogen.
- the exposed composition has maximum emission intensity at a wavelength that is greater than the excitation wavelength.
- the exposed composition has a maximum intensity at a wavelength that is between 1.1 and 1.5 times greater than an excitation wavelength of from 190 to 600 nm.
- the silicon nanoparticle compositions of the present disclosure exhibit a maximum emission wavelength that is longer prior to exposure than after exposure to the non-ambient condition. More specifically, the exposed composition has a maximum emission wavelength of from 460 to 1100 nm, alternatively from 500 to 700 nm, at an excitation wavelength of from 250 to 450 nm.
- Figure 1 is a graphical representation of a method of enhancing the photoluminescence of a silicon nanoparticle composition according to the teachings of the present disclosure
- Figure 2 is a graphical representation of the maximum emission wavelength exhibited by silicon nanoparticle compositions prepared according to the present disclosure plotted as a function of time in various non-ambient conditions;
- Figure 3 is a graphical representation of the normalized maximum emission intensity exhibited by silicon nanoparticle compositions prepared according to the teachings of the present disclosure plotted as a function of time that the composition is exposed to the non-ambient condition, i.e., an aging environment;
- Figure 4 is a graphical representation of the average particle diameter for the nanoparticles in silicon nanoparticle compositions prepared according to the teachings of the present disclosure plotted as a function of time in which the composition is exposed to the non-ambient or aging condition;
- Figure 5 is a graphical representation of the excitation and emission spectra measured for a silicon nanoparticle composition prior to or before exposure to the non-ambient condition and after exposure to or aging in the non-ambient condition plotted as a function of wavelength;
- Figures 6A-6D are graphical representations of the maximum excitation peak wavelength (Fig. 6A), the maximum emission peak wavelength (Fig. 6B), the maximum emission intensity (Fig. 6C), and the average particle diameter (Fig. 6D) exhibited by a silicon nanoparticle composition plotted as a function of exposure time or aging in a temperature/humidity chamber;
- Figure 7 is a graphical representation of the progressive shift in the emission spectrum exhibited by a silicon nanoparticle composition shown as the non- ambient aging process progresses;
- Figure 8 is a graphical representation of the luminescent quantum efficiency (LQE) of a silicon nanoparticle composition plotted as a function of exposure time or aging in the non-ambient condition;
- Figure 9 is a graphical representation of the excitation and emission spectra measured for another silicon nanoparticle composition prior to or before exposure to the non-ambient condition and after exposure to or aging in the non- ambient condition plotted as a function of wavelength;
- Figures 10A-10D are graphical representations of the maximum excitation peak wavelength (Fig. 10A), the maximum emission peak wavelength (Fig. 10B), the maximum emission intensity (Fig. IOC), and the average particle diameter (Fig. 10D) exhibited by another silicon nanoparticle composition plotted as a function of exposure time to the non-ambient condition or aging in the temperature/humidity chamber;
- Figure 11 is a graphical representation of the progressive shift in the emission spectrum exhibited by another silicon nanoparticle composition shown as the non-ambient aging process progresses;
- Figure 12 is a graphical representation of the luminescent quantum efficiency (LQE) of another silicon nanoparticle composition plotted as a function of exposure time or aging in the non-ambient condition;
- Figure 13 is a graphical representation of the emission spectra measured for another silicon nanoparticle composition prior to or before exposure to the non-ambient condition and after exposure to or aging in the non-ambient condition plotted as a function of wavelength;
- Figure 14 is a graphical representation of the emission spectra measured for another silicon nanoparticle composition prior to or before exposure to the non-ambient condition and after exposure to or aging in the non-ambient condition for 1 hour and 3 hours plotted as a function of wavelength;
- Figure 15 is a graphical representation of the emission spectra measured for another silicon nanoparticle composition prior to or before exposure to the non-ambient condition and after exposure to or aging in the non-ambient condition for 15 minutes, 30 minutes, 1 hour, 2 hours, and 3 hours plotted as a function of wavelength; and
- Figure 16 is a graphical representation of the emission spectra measured for another silicon nanoparticle composition prior to or before exposure to the non-ambient condition and after exposure to or aging in the non-ambient condition plotted as a function of wavelength.
- the present disclosure generally relates to a method of improving the photoluminescence of silicon nanoparticles and to silicon nanoparticle compositions prepared therefrom. More specifically, referring to Figure 1, the method 100 comprises providing 105 a composition in which silicon nanoparticles that have a mean particle diameter that is not greater than about 5 nanometers (nm) are dispersed in a fluid; and then exposing 110 the silicon nanoparticle composition to a non- ambient condition for a time sufficient to enhance the photoluminescence of the composition.
- the dispersion of silicon nanoparticles in the fluid refers to the nanoparticles being mixed with the fluid to such that the nanoparticles become distributed throughout the fluid without the occurrence of any substantial amount of particle agglomeration.
- the enhancement in the photoluminescence of the composition refers to (a) an increase in maximum emission intensity, (b) an increase in maximum quantum efficiency, (c) a blue shift in the wavelength associated with the maximum emission intensity, (d) a shift in the emitted light to a longer wavelength than the wavelength of the excitation light, or (e) a combination or mixture of two or more of (a)-(d).
- the silicon nanoparticle composition may be optionally subjected 115 to ambient temperature, pressure, relative humidity, and air prior to exposure 110 to the non-ambient condition. [0035] The silicon nanoparticle composition is exposed 110 to the non- ambient condition for an amount of time sufficient to increase the maximum emission intensity of the composition when excited by ultraviolet or visible light.
- the nanoparticles in the exposed composition Upon exposure to the non-ambient condition, the nanoparticles in the exposed composition exhibit increased maximum emission intensity.
- the exposed composition exhibits maximum emission intensity that is at least about 75% greater than the maximum emission intensity of the composition prior to exposure to the non-ambient condition.
- the maximum emission intensity of the composition increases by at least about 125%; alternatively, by at least about 350%; alternatively, by at least about 550% upon exposure to the non-ambient condition.
- the exposed composition has maximum emission intensity at a wavelength of at least 500 nm when exposed to light having an excitation wavelength of from about 190 to 600 nm.
- the exposed composition has a maximum emission wavelength of from about 460 to 1100 nm, alternatively from 500 to 700 nm, at an excitation wavelength of from about 250 to 450 nm.
- the exposed composition may have maximum emission intensity at a wavelength that is between 1.1 and 1.5 times greater than the excitation wavelength.
- the exposed composition has maximum intensity at a wavelength that is between 1.1 and 1.2 times greater than the excitation wavelength.
- the silicon nanoparticle composition is exposed 110 to the non- ambient condition for an amount of time sufficient to increase the luminescent quantum efficiency (LQE) of the composition.
- the luminescent quantum efficiency (LQE) of the silicon nanoparticle composition represents the ratio of the number of photons emitted by the composition to the number of photons absorbed by the composition.
- the exposed composition exhibits a LQE that is at least about 5%, alternatively at least about 10%; alternatively at least about 25%; alternatively at least about 30%.
- the increase in LQE for the silicon nanoparticle composition that occurs upon exposure to the non-ambient condition is on the order of about 100% or more; alternatively greater than about 300%; alternatively greater than about 350%.
- the silicon nanoparticle composition is exposed to the non-ambient condition for a length of time that is sufficient to enhance the photoluminescence of the composition.
- this length of time may range from a few minutes to multiple days.
- the exposure time in on the order of greater than about 20 hours and less than about 10 days.
- the silicon nanoparticle compositions prepared according to the method(s) described herein generally comprise a plurality of silicon nanoparticles having a diameter not greater than about 5 nanometers dispersed in a fluid.
- the silicon nanoparticles may consist essentially of silicon or alternatively, comprise a silicon alloy that comprises silicon and at least one element selected from germanium, boron, phosphorous, and nitrogen.
- silicon alloys that may be formed include, but are not limited to, silicon carbide, silicon germanium, silicon boron, silicon phosphorous, and silicon nitride.
- the silicon alloys may be formed by mixing at least one first precursor gas with a second precursor gas or using a precursor gas that contains the different elements.
- a precursor gas that contains the different elements.
- the silicon nanoparticles may undergo gas phase doping upon exposure to a plasma environment.
- the second precursor gas is dissociated and at least one element becomes incorporated into the silicon nanoparticles as they are nucleated.
- the silicon nanoparticles may undergo doping in the gas phase downstream of the location at which the nanoparticles are formed, but before the silicon nanoparticles are captured in a liquid.
- doped silicon nanoparticles may be produced in the capture fluid where the dopant is preloaded into the capture fluid with interaction with the nanoparticles occurring after they are captured. It is also contemplated within the scope of the present disclosure that doped nanoparticles can be formed by making contact with various gases or liquids, including, but not limited to BCI 3 , B 2 H6, P3 ⁇ 4, GeH 4 , or GeC -
- the diameter of the silicon nanoparticles is less than about five (5) nanometers and may be referred to as quantum dots. Nanoparticles on the order of 4.9 nm or 5.0 nm begin to exhibit a quantum confinement effect, the photoluminescence of which is observable in the visible spectrum.
- the concentration of the silicon nanoparticles dispersed in the fluid is such that agglomeration of the nanoparticles is minimized. This concentration may range from 0.0001 wt. % to about 50 wt. %; alternatively, from 0.001 wt. % to about 35.0 wt. %; alternatively, from 0.01 wt. % to about 20.0 wt.
- the upper limit for concentration of the nanoparticles in the fluid may be about 35.0 wt. %, 20.0 wt. %, 10.0 wt. %, 1.0 wt. %, or 0.1 wt. % depending upon the selection of the fluid.
- the lower limit for concentration of the nanoparticles in the fluid alternatively may be about 0.001 wt. % or 0.01 wt. %.
- the fluid may comprise water; a hydrocarbon solvent, such as toluene or hexane, among others; a silicone; or a mixture or combination thereof.
- the silicone fluid may be selected as one from the group of polydimethylsiloxane, phenylmethyl dimethyl cyclosiloxane, tetramethyltetraphenyltrisiloxane, pentaphenyltrimethyltri-siloxane, and mixtures or compositions thereof.
- the non-ambient condition to which the silicon nanoparticle composition is exposed 110 or subjected to may be selected 120 as one from the group of (i) elevated temperature, (ii) elevated humidity, (iii) elevated pressure exerted by an oxygen-containing gas, (iv) a hydrogen plasma, (v) molecular hydrogen, (vi) ultraviolet radiation, and (vii) a combination or mixture of two or more of (i)-(vi).
- the non-ambient condition is selected from (i)- (v) or a combination or mixture of two or more of (i)-(v).
- the elevated temperature may range from slightly above ambient or room temperature up to the boiling point of the fluid. Alternatively, ambient or room temperature is 22°C ⁇ 3°C. When the fluid is water, the upper limit for the elevated temperature is 100°C, while for other fluids, the elevated temperature may range up to about 200°C.
- the elevated humidity level may range from about 10% relative humidity (RH), alternatively from about 30% RH up to 100% RH. Elevated humidity (ii) may be used in combination with elevated temperature (i) to establish the non-ambient condition (vii) to which the silicon nanoparticle composition is exposed.
- the elevated temperature may range from above ambient temperature up to the boiling point of the fluid, while the elevated humidity is in the range of about 30% RH to 100% RH.
- the elevated pressure exerted by an oxygen-containing gas may be any pressure that is above atmospheric pressure, alternatively, the pressure may range from above atmospheric pressure to about 5,000 psig (3.458 x 10 7 Pa).
- the oxygen- containing gas is selected from oxygen, air, or a similar mixture of oxygen and inert gases.
- the pressure may alternatively range between above atmospheric pressure to about 3,000 psig (2.079 x 10 7 Pa).
- Elevated pressure (iii) exerted by an oxygen-containing gas may be used in combination with elevated temperature (i) to establish the non-ambient condition (vii) to which the silicon nanoparticle composition is exposed.
- the elevated temperature ranges from above ambient temperature to the boiling point of the fluid and the elevated pressure ranges from above atmospheric pressure to about 5,000 psig (3.458 x 10 7 Pa), alternatively, to about 3,000 psig (2.079 x 10 7 Pa).
- the silicon nanoparticle compositions are subjected to a hydrogen plasma (e.g., atomic hydrogen) and molecular hydrogen, respectively.
- a hydrogen plasma e.g., atomic hydrogen
- the composition may be exposed to non-ambient condition (vii) by exposing the composition in order, first to a hydrogen plasma (iv) and then to a combination of elevated temperature (i) and elevated humidity (ii).
- hydrogen plasma comprises a combination of hydrogen and argon.
- the silicon nanoparticle compositions are subjected to ultraviolet radiation.
- a source of ultraviolet radiation may comprise a high-pressure mercury lamp, medium-pressure mercury lamp, Xe-Hg lamp, or a deep UV lamp.
- the wavelength of the ultraviolet radiation may vary within the ultraviolet spectrum, as readily understood in the art.
- the dosage of the ultraviolet radiation may vary based on the desired qualities of the silicon nanoparticle compositions. Subjecting the silicon nanoparticle compositions to ultraviolet radiation is distinguished from ultraviolet radiation conventionally utilized for photoinitiating a reaction.
- the ultraviolet radiation is generally utilized solely for improving photoluminescent and/or optical properties of the silicon nanoparticle compositions, and not for initiating curing within the silicon nanoparticle compositions.
- non- ambient condition (vi) may be utilized in combination with any of non-ambient conditions (i)-(v).
- non-ambient condition (vi) is utilized in combination with non-ambient condition (iv), i.e., ultraviolet radiation is utilized in combination with hydrogen plasma.
- the silicon nanoparticle compositions may be subjected to ultraviolet radiation before, during, and/or after subjecting the silicon nanoparticle compositions to hydrogen plasma.
- subjecting the silicon nanoparticle compositions to ultraviolet radiation in conjunction with hydrogen plasma provides improved optical properties of the silicon nanoparticles along with improved photoluminescent properties.
- Wavelengths of the ultraviolet radiation may vary based on the presence or absence of other optional gasses and/or elements, including those associated with certain sources of ultraviolet radiation and/or those associated with the hydrogen plasma.
- subjecting the silicon nanoparticle compositions to ultraviolet radiation may result in the atomic emission of ultraviolet light from the hydrogen and/or argon as well, which increases exposure of the silicon nanoparticle compositions to the ultraviolet radiation.
- the method 100 of the present disclosure may incorporate silicon nanoparticles that are made by any method known to one skilled in the art, including, but not limited to the use of a gas phase reaction 125.
- the method 100 as described throughout the present disclosure uses a silicon nanoparticle composition prepared by forming nanoparticles in a high frequency, low pressure plasma reactor and collecting said particles in the reactor with a capture fluid is done in order to more fully illustrate the concept and is not intended to limit the disclosure.
- the incorporation and use of nanoparticles in a fluid in conjunction with other types of processes or methods of preparing nanoparticles is contemplated to be within the scope of the disclosure.
- the photoluminescent silicon nanoparticles can be prepared by providing at least one reactant gas mixture to a plasma reactor system.
- This reactant gas mixture may comprise a first reactive precursor gas and optionally, an inert gas.
- the first reactive precursor gas may comprise from about 0.1 % to about 50% of the total volume of the reactant gas mixture.
- the first reactive precursor gas may be selected as one from the group of silanes, disilanes, halogen-substituted silanes, halogen-substituted disilanes, C1-C4 alkyl silanes, Q to C 4 alkyldisilanes, and mixtures thereof.
- the first reactive precursor gas examples include SiH 4 , SiCl 4 , HSiCl 3 , and H2S1CI2, among others or combinations thereof.
- the optional inert gas include argon, xenon, neon, or a mixture thereof. When present in the reactant gas mixture, the inert gas may comprise from about 1% to about 99% of the total volume of the reactant gas mixture.
- the reactant gas mixture may also comprise a second precursor, which itself can comprise from about 0.1 to about 49.9 volume % of the reactant gas mixture; hydrogen gas that is present in an amount ranging from about 1 to 10 volume % of the reactant gas mixture; or a mixture thereof.
- the second precursor gas may comprise BCI 3 , B 2 H6, P3 ⁇ 4, GeH 4 , GeCl 4 , or other gases that contain carbon, germanium, boron, phosphorous, or nitrogen.
- the combination of the first reactive precursor gas and the second precursor gas together make up from about 0.1 to about 50% of the total volume of the reactant gas mixture.
- the operating pressure in the reactor and collection chamber typically ranges from about 1 to about 5 millitorr.
- the mean particle diameter exhibited by the nanoparticles that are formed therein can be controlled through adjustment of various operating parameters, including but not limited to frequency and ion density, mass flow rate of the reactant gas mixture, the use of pulsation, and adjustment of the orifice size associated with the plasma discharge jet.
- the use of high frequency plasma yields better power coupling and produces a discharge with higher ion energy and density.
- the pulsation of the plasma enables one skilled in the art to directly set the residence time for particle nucleation and, thereby, control the particle size distribution and agglomeration kinetics in the plasma.
- the power may be supplied via a variable frequency radio frequency power amplifier that is triggered by an arbitrary function generator to establish the high frequency.
- the radio frequency power may be capacitively coupled or inductively coupled into the plasma.
- the silicon nanoparticle composition can be prepared by collecting the nanoparticles in a capture fluid that is present in the plasma reactor system.
- the capture fluid may be selected to allow nanoparticles to be absorbed and dispersed into the fluid as they are collected, thus forming a dispersion or suspension of nanoparticles in the capture fluid.
- the rate of absorption of the nanoparticles into the capture fluid can be adjusted by the degree to which the capture fluid is agitated.
- Various forms of agitation include rotational stirring, inversion, and ultrasonication, among others.
- siloxane located 5 cm downstream of the orifice
- Deposition rate was 0.01 wt. % of silicon nanoparticles per five (5) minutes of run time.
- Each of the samples is aged under ambient air by leaving them in the lab for 3, 12, or 21 days. Each sample is then placed into a 35 mL quartz round bottom dish and subjected to plasma-treated post processing using the following process parameters: 750 seem 3 ⁇ 4 and 100 seem 0 2 ; a chuck temperature of 80°C; a pressure of 7.5 Torr; and a plasma power of 120 W at 13.56 MHz. Each sample is subjected to four 5 minute runs with mixing after each five minute cycle for a total of 20 minutes exposure to the plasma.
- the samples are then subjected to temperature and humidity post processing by placing each of the 35 mL quartz round bottom dishes in a temperature and humidity chamber for 168 hours. A total of 0.7 g of each sample is removed from each dish after every 24 hours for use in measuring their excitation and emission spectra.
- the removed samples are placed in a quartz cuvette and an excitation and/or emission spectrum measured via a Fluorolog-2 spectrofluorometer. The excitation spectrum is measured from 250 - 500 nm @ 1 nm step with an integration time of 0.1 seconds with the emission held at 700 nm with a 570 nm filter placed between the sample and the emission detector.
- the emission spectrum is measured from 450 - 850 nm @ 1 nm step with an integration time of 0.1 seconds with excitation at 365 nm and a 400 nm filter placed between the sample and the emission detector.
- An Ocean Optics 4000USB spectrometer with an integrated sphere is used to obtain the luminescent quantum efficiency.
- a 395 nm LED is driven at 10.1 mA as the excitation source.
- Three spectra of each sample are recorded.
- the reference polydimethlysiloxane sample (PDMS - 100 est) that is used as the background for comparison undergoes the same treatment conditions without silicon nanoparticles.
- the emission Spectrum is fitted to a Gaussian distribution according to
- Equation 1 in order to obtain the maximum emission wavelength, standard deviation, full width at half maximum, intensity, and adjusted R 2 of the fit.
- the particle size or diameter is determined by transformation of the emission spectrum to particle size or diameter and fitted with a Log normal distribution according to Equations 2 and 3. The mean particle diameter, standard deviation, and adjusted R 2 of the fit are recorded.
- the luminescent Quantum Efficiency is then obtained by determining the integrated total photon count for each spectrum, absorption (350 - 450 nm) and emission (480 - 850 nm). The total photon count for the three spectra are then averaged and used to calculate the LQE according to Equation 4. [0067]
- LQE luminescent Quantum Efficiency
- a total of 0.01 wt. % of silicon nanoparticles dispersed in 14 g of 100 est PDMS is aged at different non-ambient conditions for 14 days.
- the control condition (Run No. 0) represents a vial of a silicon nanoparticle composition in PDMS that is left open to lab air for the 14 days.
- Run No. 1 represents a "moist" atmosphere condition created by a silicon nanoparticle composition being sealed with in a jar having an air and water vapor atmosphere.
- a "dry" air condition is created by bubbling clean, dry compressed air into a silicon nanoparticle composition in a sealed vial with the excess air being removed via a vent.
- a "moist” air condition is established by bubbling clean dry compressed air through a sealed vial containing water. The head space of the water/air vial is then bubbled into a sealed vial containing a silicon nanoparticle composition.
- a "dry" heat condition is created by placing a silicon nanoparticle composition into an oven at 80°C.
- a "moist” heat condition is established in which a silicon nanoparticle composition is placed into an oven at 80°C along with water.
- Each of the samples (Run No.'s 1-5) are then periodically removed from their respective environments and measured with the Fluorolog-2 spectrofluorometer to obtain the maximum emission wavelength, maximum emission intensity, and average particle diameter as functions of the time in the aging environment.
- each silicon nanoparticle composition is plotted as a function of time in the aging or non-ambient environment.
- the emission of the silicon nanoparticles is shown to blue shift for all cases (Run No.'s 0-5) as the particles oxidize due to oxygen diffusing through the PDMS fluid.
- the degree of the blue shift that occurs for the silicon nanoparticle composition exposed to non-ambient conditions (Run No.'s 1-5) is greater than that occurs in the control (Run No. 0).
- the least amount of change for the different non-ambient conditions tested in this Example 1 is the use of "dry" air as shown in the comparison of Run No. 2 with the control (Run No. 0).
- the highest rate of oxidation occurs when the silicon nanoparticle composition is subjected to a non- ambient moist heat condition (Run No. 5).
- a substantial change in the maximum emission wavelength results after exposure to the non-ambient condition for greater than about 24 hours, alternatively, greater than about 36 hours, alternatively, greater than about 48 hours with a smaller degree of change occurring even after about 14 days.
- the average particle diameter for the nanoparticles in each silicon nanoparticle composition is plotted as a function of time in which the composition is exposed to the non-ambient or aging condition.
- the average particle diameter is calculated via transforming the emission spectrum to a particle diameter spectrum and fitting the curves to a log normal distribution as previously described using Equations 2 and 3.
- the average particle diameter decreases as a function of time. This decrease in average particle diameter is a result of the nanoparticles' surface being oxidized.
- the magnitude of the decrease in average particle size is smallest with the control (Run No. 0) and for exposure to "dry" air (Run No. 2).
- the moist heat condition (Run No. 5) yields the greatest decrease in average particle diameter.
- the order of decrease in particle size for each of the Run No.'s 1-5 closely matches the shift in the emission spectrum measured for the silicon nanoparticle compositions as shown in Figure 2.
- a total of 0.01 wt. % of silicon nanoparticles are dispersed in 14 g of
- the silicon nanoparticle composition (Run No. 6) is allowed to stand undisturbed for 21 days prior to exposure to post processing.
- the silicon nanoparticle composition then underwent a post synthesis plasma treatment using the conditions listed above in Example 1.
- the silicon nanoparticle composition (Run No. 6) then is placed in a temperature and humidity chamber at 65°C and 85% relative humidity for 168 hours. Samples are removed and measured with the Fluorolog-2 spectrofluorometer and the Ocean Optics spectrometer or integrating sphere at intervals of 24 hours, 48 hours, 120 hours, 144 hours, and 168 hours of aging in the non- ambient temperature/humidity conditioning chamber.
- the maximum excitation wavelength, the maximum emission wavelength, the maximum emission intensity, and the average particle diameter exhibited by the silicon nanoparticle composition (Run No. 6) is plotted as a function of exposure time to the non-ambient condition, i.e., aging in the temperature/humidity chamber.
- the excitation peak ( Figure 6A) exhibited by silicon nanoparticle demonstrates a shift to higher energy during the treatment.
- the maximum emission wavelength of the silicon nanoparticle composition ( Figure 6B) undergoes a blue shift due to the oxidation of the nanoparticles.
- the maximum emission intensity of the silicon nanoparticle composition (Figure 6C) undergoes a six-fold increase as a result of exposure to the non-ambient condition.
- the average particle diameter calculated from the emission spectrum of the silicon nanoparticles in the composition ( Figure 6D) decreases from about 3.7 nanometers to less than 3.0 nanometers during the aging process.
- FIG. 7 the progressive shift in the emission spectrum exhibited by silicon nanoparticle composition (Run No. 6) is shown as the aging process progresses.
- a quick blue shift in wavelength and a substantial increase in intensity of the emission occurs (compare 0 hours with 24 hour exposure curves) when the silicon nanoparticle composition is initially exposed to the non-ambient temperature and humidity condition or environment.
- a much slower increase in maximum emission intensity and shift in wavelength occurs upon continued exposure to the non-ambient condition (see 48-168 hour curves).
- the maximum emission intensity of the composition increases by about 350% after 24 hours of exposure; alternatively, about 450% after 48 hours of exposure; and alternatively, about 550% after about 120 hours of exposure.
- the luminescent quantum efficiency (LQE) of the silicon nanoparticle composition (Run No. 6) is plotted as a function of exposure time or aging in the non-ambient condition.
- the LQE is calculated from the spectrum measured using the previously described integrating sphere procedure.
- a substantial increase in the LQE is observed upon initial exposure of the silicon nanoparticle composition to the non-ambient condition. For example, within the first 24 hours of exposure a 300% increase in luminescent quantum efficiency is observed to occur. Over the entire exposure time (168 hours) to the non-ambient condition approximately a 600% increase in LQE is observed to occur.
- a total of 0.01 wt. % of silicon nanoparticles are dispersed in 14 grams of PDMS (100 est) under the conditions stated above (see Table 1).
- the silicon nanoparticle compositions are allowed to sit under ambient conditions for three days prior to any post processing.
- the silicon nanoparticle compositions in this example are not subjected to the post synthesis plasma treatment as previously described for the compositions in Examples 1 and 2.
- the silicon nanoparticle composition (Run No. 7) in this example is then placed in a temperature and humidity chamber at 85°C and 65% relative humidity for 168 hours.
- Samples are removed and measured with the Fluorolog-2 spectrofluorometer and the Ocean Optics spectrometer or integrating sphere at intervals of 24 hours, 48 hours, 72 hours, 96 hours, and 168 hours of aging in the non-ambient temperature/humidity conditioning chamber.
- the maximum excitation wavelength, the maximum emission wavelength, the maximum emission intensity, and the average particle diameter exhibited by the silicon nanoparticle composition (Run No. 7) is plotted as a function of exposure time to the non-ambient condition, i.e., aging in the temperature/humidity chamber.
- the excitation peak ( Figure 10A) exhibited by silicon nanoparticle demonstrates a shift to higher energy during the treatment.
- the maximum emission wavelength of the silicon nanoparticle composition ( Figure 10B) undergoes a blue shift due to the oxidation of the nanoparticles.
- the maximum emission intensity of the silicon nanoparticle composition (Figure IOC) undergoes a seventeen-fold increase as a result of exposure to the non-ambient condition.
- the average particle diameter calculated from the emission spectrum of the silicon nanoparticles in the composition ( Figure 10D) decreases from greater than 4.0 nanometers to less than 2.8 nanometers during the aging process.
- the luminescent quantum efficiency (LQE) of the silicon nanoparticle composition (Run No. 7) is plotted as a function of exposure time or aging in the non-ambient condition.
- the LQE is calculated from the spectrum measured using the previously described integrating sphere procedure.
- a substantial increase in the LQE is observed upon initial exposure of composition to the non-ambient condition. For example, within the first 24 hours of exposure approximately a 300% increase in luminescent quantum efficiency is observed to occur. However, over the entire exposure time (168 hours) to the non-ambient condition approximately only a 350% increase in LQE is observed to occur.
- the overall increase in luminescent quantum efficiency for this silicon nanoparticle composition (Run No.
- the post plasma hydrogen treatment creates atomic hydrogen that diffuses into the PDMS and can passivate defects, such as P , Pbo, and P i defects, that may occur at a silicon / silicon oxide interface.
- a total of 0.03 wt. % silicon nanoparticles are dispersed in PDMS (100 est) under the conditions stated above (see Table 1).
- the silicon nanoparticle composition (Run No. 8) is stored in a nitrogen filled glove box to limit exposure to air (i.e., oxygen). Then a portion (i.e., about 60 ml) of the composition is placed in a pressure reactor and pressurized to 1500 psig (1.044 x 10 7 Pa) with ultrahigh purity 0 2 gas. In the presence of this non-ambient condition, the composition is stirred at 600 rpm and held at 40°C for 168 hrs.
- the emission spectra measured for the silicon nanoparticle composition (Run No. 8) prior to or before exposure to the non- ambient condition (Control, 0 hours) and after exposure to or aging in the non- ambient condition for 168 hours is plotted as a function of wavelength.
- a noticeable blue shift in wavelength, as well as an increase in intensity is observed for the aged composition.
- the blue shift and increase in intensity signifies the occurrence of oxidation related to the surface of the particles in the fluid, while still retaining strong luminescence.
- a total of 0.03 wt. % silicon nanoparticles are dispersed in PDMS (100 est) under the conditions stated above (see Table 1).
- the silicon nanoparticle composition (Run No. 9) is stored in a nitrogen filled glove box to limit exposure to air (i.e., oxygen). Then a portion of the composition is placed in a pressure reactor and pressurized to 190 psig (1.411 x 10 6 Pa) with ultrahigh purity 0 2 gas. In the presence of this non-ambient condition, the composition is stirred at 600 rpm and held at 60°C for 3 hrs.
- the emission spectra measured for the silicon nanoparticle composition (Run No. 9) prior to or before exposure to the non- ambient condition (Control, 0 hours) and after exposure to or aging in the non- ambient condition for 1 hour and 3 hours is plotted as a function of wavelength.
- a noticeable blue shift in wavelength, as well as an increase in maximum emission intensity is observed for the aged composition. More specifically, maximum emission intensity is observed to increase by about 125% after 1 hour exposure of the composition to the non-ambient condition as shown in comparison to the emission intensity of the initial sample (0 hours exposure). A slight decrease then occurs upon continued exposure (compare 1 hour and 3 hour curves).
- a total of 0.03 wt. % silicon nanoparticles are dispersed in PDMS (100 est) under the conditions stated above (see Table 1).
- the silicon nanoparticle composition (Run No. 10) is stored in a nitrogen filled glove box to limit exposure to air (i.e., oxygen). Then a portion (i.e., 60 ml) of the composition is placed in a pressure reactor and pressurized to 190 psig (1.411 x 10 6 Pa) with ultrahigh purity 0 2 gas. In the presence of this non-ambient condition, the composition is stirred at 600 rpm and held at 120°C for 3 hours.
- the emission spectra measured for the silicon nanoparticle composition (Run No. 10) prior to or before exposure to the non- ambient condition (Control, 0 hours) and after exposure to or aging in the non- ambient condition for 15 minutes, 30 minutes, 1 hour, 2 hours, and 3 hours is plotted as a function of wavelength. A noticeable blue shift in wavelength is observed for the aged composition.
- the overall emission intensity decreases as compared to exposure of a similar composition (Run No. 9, Example 5) to a lower exposure temperature.
- the maximum intensity for Run No. 10 is observed to occur at 1 hour, even though in this case the overall measured intensity is lower than the initial intensity exhibited by the silicon nanoparticle composition (control, 0 hours).
- a total of 0.03 wt. % silicon nanoparticles are dispersed in PDMS (100 est) under the conditions stated above (see Table 1).
- the silicon nanoparticle composition (Run No. 11) is stored in a nitrogen filled glove box to limit exposure to air (i.e., oxygen).
- a portion (i.e., 60 ml) of the composition is placed in a pressure reactor and pressurized to 190 psig (1.411 x 10 6 Pa) with ultrahigh purity 0 2 gas.
- the composition is stirred at 600 rpm and held at 140°C for 10 minutes, creating a pressure of 25 psig (2.737 x 10 5 Pa).
- the emission spectra measured for the silicon nanoparticle composition (Run No. 11) prior to or before exposure to the non- ambient condition (control, 0 hours) and after exposure to or aging in the non-ambient condition for 10 minutes is plotted as a function of wavelength.
- a noticeable blue shift in wavelength, as well as an increase in maximum emission intensity of about 75% (8 counts -> 14 counts) is observed for the aged composition over the short interval of exposure to the non-ambient condition.
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EP13747924.2A EP2880125A1 (en) | 2012-07-30 | 2013-07-30 | Method of improving photoluminescence of silicon nanoparticles |
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WO2010027959A1 (en) | 2008-09-03 | 2010-03-11 | Dow Corning Corporation | Low pressure high frequency pulsed plasma reactor for producing nanoparticles |
US20110204290A1 (en) * | 2008-09-01 | 2011-08-25 | National University Corporation Tokyo University Of Agriculture And Technology | Silicon-based blue-green phosphorescent material of which luminescence peak can be controlled by excitation wavelength and process for producing silicon-based blue-green phosphorescent material |
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WO2009047995A1 (en) * | 2007-10-13 | 2009-04-16 | Konica Minolta Medical & Graphic, Inc. | Semiconductor nanoparticle |
US20110204290A1 (en) * | 2008-09-01 | 2011-08-25 | National University Corporation Tokyo University Of Agriculture And Technology | Silicon-based blue-green phosphorescent material of which luminescence peak can be controlled by excitation wavelength and process for producing silicon-based blue-green phosphorescent material |
WO2010027959A1 (en) | 2008-09-03 | 2010-03-11 | Dow Corning Corporation | Low pressure high frequency pulsed plasma reactor for producing nanoparticles |
WO2011109299A1 (en) | 2010-03-01 | 2011-09-09 | Dow Corning Corporation | Photoluminescent nanoparticles and method for preparation |
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